The current thin-film photovoltaic technologies can be classified by the different materials used for the light absorption in a solar cell. These materials include amorphous and polycrystalline silicon, CdTe, CuInxGa1-xSe2(CIGS), GaAs, and photosensitive organic dyes. A transformative technology may emerge when a new and better material is being discovered for thin-film photovoltaic applications.
D. Scaife, P. Weller, and W. Fisher, reported an early study on the structural information of CsSnI3 compound in form of powders, J. Solid State Chem. 9, 308 (1974).
P. Mauersberger and F. Huber, synthesized a yellow, needle-like CsSnI3 microcrystal, and studied its crystal structure, Acta Cryst. B 36, 683 (1980).
K. Yamada, S. Funabiki, H. Horimoto, T. Matsui, T. Okuda, and S. Ichiba, reported the polymorph nature of CsSnI3compound, Chem. Lett. (The Chemical Society of Japan) 20, 801 (1991).
The black polymorph of CsSnI3 could be obtained through a phase transition from the yellow polymorph CsSnI3 by increasing its temperature above 425° K. It was further demonstrated by differential thermal analysis and X-ray diffraction that during the cooling of the black CsSnI3 from 450° K, its ideal cubic perovskite structure (B-α) deformed to a tetragonal structure (B-β) at 426° K, and became an orthorhombic structure (B-γ) below 351° K. Experimental studies of electrical and optical properties of this compound have been hindered by lack of high quality CsSnI3 samples either in bulk or thin film format.
Aiming at the unique properties of hybrid organic-inorganic perovskites based on tin halides, I. Borriello, G. Gantel, and D. Ninno, recently calculated band structures of B-α, B-β, and B-γ from the first principles using the crystal structures published by Yamada et al., Phys. Rev. B 77, 235214 (2008). It was concluded that all three structures had direct band-gap (Eg) at Z, R, and Γ points for B-α, B-β, and B-γ, respectively, with Eg (B-α)<Eg (B-β)<Eg (B-γ).
A need still exists in the industry for developing low cost synthesis methods for CsSnI3 thin films, especially in large scale. The successful implementation of these materials for various applications requires a detailed understanding of both their processing and materials properties.